Hybrid vehicles usually have two different drive units, for example, an internal combustion engine, which is operated using a fuel, and an electric machine, which draws its electrical power from an electrical storage device. Hybrid vehicles may be driven temporarily by the electric machine alone. However, if no more electrical power is available, the internal combustion engine is started and the vehicle is driven with this engine. A generator may be driven while the internal combustion engine is running. This generator in turn generates electrical power, which is stored in the electrical storage device. Electrical operation of the vehicle is then also possible.
There are believed to be various methods for starting the internal combustion engine. German patent document DE 196 45 943 proposes a starter unit, which allows two different starting methods. One starting method is a pulse start and the other is a direct start. The pulse start may be employed when the engine is cold, using the energy of a flywheel, and the direct start is used when the engine is hot, for example, at a stoplight. The best starting method in each case is thus selected automatically as a function of the temperature of the internal combustion engine.